JP5871186B2 - Non-aqueous electrolyte secondary battery active material, method for producing the active material, non-aqueous electrolyte secondary battery electrode, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to an active material for a non-aqueous electrolyte secondary battery, a method for producing the active material, and a non-aqueous electrolyte secondary battery using the active material.

Conventionally, LiCoO ₂ is mainly used as a positive electrode active material in a non-aqueous electrolyte secondary battery. However, the discharge capacity was about 120 to 130 mAh / g.

As a positive electrode active material for nonaqueous electrolyte secondary batteries, a solid solution of LiCoO ₂ and other compounds is known. Li [Co _1-2x Ni _x Mn _x ] O ₂ (0 <x ≦ 1/2) having a α-NaFeO ₂ type crystal structure and being a solid solution of three components of LiCoO ₂ , LiNiO ₂ and LiMnO ₂ Was announced in 2001. LiNi _1/2 Mn _1/2 O ₂ and LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , which are examples of the solid solution, have a discharge capacity of 150 to 180 mAh / g, and are charged and discharged. Excellent cycle performance.

For the so-called “LiMeO ₂ type” active material as described above, the composition ratio Li / Me of lithium (Li) with respect to the ratio of transition metal (Me) is larger than 1, for example, Li / Me is 1.25 to 1.6. So-called “lithium-rich” active materials are known. Such a material can be expressed as Li _{1 + α} Me _1-α O ₂ (α> 0). Here, when the composition ratio Li / Me of lithium (Li) with respect to the ratio of the transition metal (Me) is β, β = (1 + α) / (1-α), and thus, for example, Li / Me is 1.5. In this case, α = 0.2.

Patent Document 1 discloses a kind of active material such as Li [Li _1/3 Mn _2/3 ] O ₂ , LiNi _1/2 Mn _1/2 O ₂ and LiCoO ₂ as a solid solution. An active material that can be represented is described. In addition, as a method for manufacturing a battery using the active material, a potential change that appears in the positive electrode potential range of 4.3 V (vs. Li ^/ Li ⁺ ) to 4.8 V or less (vs. Li ^/ Li ⁺ ). This is a case where a charging method in which the maximum potential of the positive electrode at the time of charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less is adopted by providing a manufacturing process that performs charging at least in a relatively flat region. However, it is described that a battery capable of obtaining a discharge capacity of 177 mAh / g or more can be manufactured.

Thus, unlike the so-called “LiMeO ₂ type” positive electrode active material, the so-called “lithium-excess type” positive electrode active material has a relatively high potential exceeding 4.3 V, particularly 4.4 V or more, at least in the first charge. A characteristic is that a high discharge capacity can be obtained by carrying out the process to a potential of. However, such a “lithium-rich” positive electrode active material does not have sufficient high rate discharge characteristics. In particular, the “lithium-rich” positive electrode active material tended to have a higher resistance in the low SOC region from the middle to the end of the discharge than the “LiMeO ₂ type” active material.

  In addition, it is known that the invention improves various properties by changing the composition of the lithium transition metal composite oxide on the surface and inside of the positive electrode active material particles (see, for example, Patent Documents 2 to 8).

Patent Document 2 discloses that “general formula: LiMO ₂ (wherein M is one or more metal elements including at least one transition metal element selected from the group consisting of Co, Ni, and Mn”). lithium transition metal composite oxide represented by some), a positive electrode active material for a lithium secondary battery comprising a solid solution particles of lithium manganese oxide represented by Li ₂ MnO _3, in the center of the solid-solution particles the closer the _Li 2 concentration of MnO ₃ is constituted higher than the concentration of the LiMO _2, and, the closer to the outer surface of the solid solution particles, the concentration of the LiMO ₂ is than the concentration of the _Li 2 MnO ₃ The positive electrode active material for a lithium secondary battery, characterized in that it has a concentration gradient that is configured to be high. "(Claim 1) The invention of" LiMO ₂ and Li ₂ An excellent load characteristic (characteristic that maintains a high capacity even during a large current discharge) or cycle characteristic (repeated charge / discharge), which is a solid solution with MnO ₃ and suppresses elution of manganese even after repeated high-rate charge / discharge Lithium manganese oxidation represented by Li ₂ MnO ₃ is intended to provide a positive electrode active material for a lithium secondary battery having a characteristic of maintaining a high capacity) (paragraph [0007]). Since the product particles are used as starting materials (claim 4, example), the load characteristics (high rate discharge characteristics) are not sufficiently improved.

In Patent Document 3, the composition of Li _x Mn _{2 -y 2} Ni _{y 2} O ₄ (0.95 ≦ x2 ≦ 1.10, 0.45) is formed on or near the particle surface of Li—Mn composite oxide particles serving as a nucleus. ≦ y2 ≦ 0.55), or Li _x3 Mn _1-y3 Fe _y3 PO ₄ (0.98 ≦ x3 ≦ 1.10, 0 <y3 ≦ 0.30) at least one Li—Mn compound particle The invention of the positive electrode active material particle powder for a non-aqueous electrolyte secondary battery coated with or present (claim 1) is described, but this invention states that “the charge / discharge capacity during high-voltage charging is large, ”Providing positive electrode active material particle powder for non-aqueous electrolyte secondary battery with excellent discharge efficiency” (paragraph [0001]), not a problem to improve high-rate discharge characteristics, Also, cobalt on the particle surface or in the vicinity of the surface It does not contain.

Patent Document 4 includes “a main electrode active material particle containing lithium, and a coated electrode active material particle containing lithium whose particle size is one-tenth of the main electrode active material, and the coating containing lithium” The electrode active material particle covers the outer layer surface of the main electrode active material particle and is sintered, and the invention of claim 1 describes and implements the composite electrode active material of a lithium battery. As an example, it is shown that the surface of LiNi _0.75 Co _0.2 Mg _0.05 O ₂ is coated with LiCoO ₂ and the surface of LiMn ₂ O ₄ is coated with LiCoO ₂ (paragraph [0016]. , [0017]) is only described as "This composite material can improve battery conductivity and discharge efficiency and extend cycle life" (paragraph [0010]). rate No description of electrostatic characteristics, not the active material is also shown to as "lithium-excess."

Patent Document 5 discloses that a mixture of a lithium salt and a precursor for a positive electrode active material in which the surface of nickel-cobalt composite hydroxide particles is coated with a sodium-containing cobalt compound layer containing an amorphous portion is contained in an oxidizing atmosphere. The positive electrode active material obtained by firing at a. ”(Claim 5) is described, wherein“ the inside of the positive electrode active material is Li _x Ni _1-y Co _y O ₂ (0.9 ≦ x ≦ 1.1, 0 <y ≦ 0.5), and the surface portion of the positive electrode active material is LixNi _1- AB Co _A Na _B O ₂ (0.9 ≦ x ≦ 1.1, 0 <A ≦ 1.0, 0 <B ≦ 0.02), and y <A ”(Claim 6) However, according to the present invention, “high capacity, It is merely described that a non-aqueous electrolyte secondary battery that is relatively inexpensive and excellent in safety can be obtained ”(paragraph [0028]), there is no description about high-rate discharge characteristics, and nickel cobalt It is not shown that manganese is contained in the composite oxide.

Patent Document 6 states that “a battery active material, which is composed of at least two types of active material, the material in the particle has a core-shell type structure, The battery active material is characterized in that the active material in the shell part has a high output. "(Invention 1) is described, and the active material in the core part is a part of nickel in LiNiO ₂ is manganese. In addition, the active material material of the shell portion is one in which a part of manganese in LiMn ₂ O ₄ is substituted with cobalt or the like (claims 6 and 9). However, an object of the present invention is to provide a battery active material that can fully utilize the characteristics of each active material having different output performance and capacity performance, and a lithium ion secondary battery using the battery active material. ”(Paragraph [000 6]), and is not intended to improve the high-rate discharge characteristics, and does not suggest that the active material is “lithium-excess type”.

In Patent Document 7, the active material particles include at least a first lithium nickel composite oxide that constitutes a core portion thereof, and the first lithium nickel composite oxide is Li _x Ni _{1 -yz} Co _y Me _z O _2. (However, 0.85 ≦ x ≦ 1.25, 0 <y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 <y + z ≦ 0.75, the element Me is from Al, Mn, Ti, Mg and Ca. At least one selected from the group consisting of: a surface layer portion of the active material particles containing nickel oxide or a second lithium nickel composite oxide having a NaCl-type crystal structure; Further includes an element M that is not incorporated in the crystal structure of the first lithium-nickel composite oxide, and the element M includes Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo and Selected from the group consisting of Sn The invention of at least one active material particle of a lithium ion secondary battery (Claim 1) is described, and this invention describes "safety at the time of an internal short circuit without inhibiting high rate characteristics at low temperatures. further aims to increase "(paragraph [0012]) _{imply, Li x Ni 1-yz Co} y Me z O 2 and has a starting material (claim 6, example) although, NaCl-type crystal structure Since the activity of the nickel oxide or the second lithium nickel composite oxide having low is low, the high rate characteristics (high rate discharge characteristics) are not excellent, and the surface layer of the particles contains a large amount of cobalt. Absent.

Patent Document 8 includes “secondary particles in which primary particles, which are lithium composite oxide particles in which at least nickel (Ni) and cobalt (Co) are dissolved as transition metals, are aggregated, The average composition is represented by chemical formula 1, the abundance of cobalt (Co) increases from the center of the primary particle toward the surface, and among the primary particles constituting the secondary particle, the surface of the secondary particle A positive electrode active material in which the abundance of cobalt (Co) in the primary particles present in the vicinity is greater than the abundance of cobalt (Co) in the primary particles present in the vicinity of the center of the secondary particles.
Formula _{1] Li x Co y Ni z} M 1-yz O ba X a
(In the formula, M represents boron (B), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), titanium (Ti), chromium (Cr), manganese (Mn ), Iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), yttrium (Y), zirconium (Zr), molybdenum (Mo), silver (Ag), barium (Ba) ), Tungsten (W), indium (In), strontium (Sr), tin (Sn), lead (Pb), and antimony (Sb), and X is a halogen element. x, y, z, a and b are 0.8 <x ≦ 1.2, 0 <y ≦ 0.5, 0.5 ≦ z ≦ 1.0, 1.8 ≦ b ≦ 2.2, 0, respectively. ≦ a ≦ 1.0.) ”(Claim 1) However, the present invention aims to provide a positive electrode active material, a positive electrode for a nonaqueous electrolyte battery, and a nonaqueous electrolyte battery that simultaneously contribute to an increase in capacity and suppression of gas generation. Paragraph [0013]), which is not intended to improve the high rate discharge characteristics, and does not specifically describe the inclusion of Mn in the lithium composite oxide particles.

JP 2010-086690 A JP 2011-134670 A JP 2011-134708 A JP 2011-86603 A JP 2010-80231 A JP 2007-213866 A JP 2006-302880 A JP 2012-18827 A

  An object of the present invention is to provide an active material for a nonaqueous electrolyte secondary battery excellent in high-rate discharge characteristics, a method for producing the active material, and a nonaqueous electrolyte secondary battery using the active material.

  The configuration and operational effects of the present invention will be described with the technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or experimental examples are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The present invention employs the following means in order to solve the above problems.
(1) Lithium transition having an α-NaFeO ₂ type crystal structure and an average composition represented by a composition formula Li _{1 + α} Me _1-α O ₂ (Me is a transition metal containing Co, Ni and Mn, α> 0) An active material for a non-aqueous electrolyte secondary battery containing a metal composite oxide, wherein the lithium transition metal composite oxide is a particle having a core and a coating portion, and the cobalt concentration in the coating portion is cobalt in the core Higher than the concentration, the manganese concentration of the coating portion is lower than the manganese concentration of the core, the coating portion has a gradient of cobalt concentration, and the particle surface position is 0 and the center position is 1. An active material for a non-aqueous electrolyte secondary battery, wherein the starting point of the cobalt concentration gradient region from the surface is 0.1 to 0.5.
(2) The nonaqueous electrolyte secondary according to (1), wherein a ratio of cobalt present in the coating portion is 3 to 10% in terms of a molar ratio with respect to an amount of the transition metal present in the core. Battery active material.
(3) The nonaqueous electrolyte according to (1) or (2) above, wherein the particle size at which the cumulative volume in the particle size distribution of the secondary particles of the lithium transition metal composite oxide particles is 50% is 8 μm or less. Active material for secondary batteries.
(4) The method for producing an active material for a non-aqueous electrolyte secondary battery according to any one of (1) to (3 ) above, wherein the first aqueous solution of a transition metal compound containing cobalt, nickel, and manganese is used. During the preparation of the precipitation precursor, cobalt from the particle surface is added by adding a second aqueous solution of a transition metal compound containing cobalt, nickel and manganese, having a higher cobalt concentration than the first aqueous solution and a lower manganese concentration. The lithium transition metal composite oxide is manufactured through a step of producing coprecipitation precursor particles of a transition metal compound having a concentration gradient region, a step of mixing the coprecipitation precursor particles with a lithium compound, and firing. The manufacturing method of the active material for nonaqueous electrolyte secondary batteries characterized by the above-mentioned.
(5) An electrode for a non-aqueous electrolyte secondary battery comprising the active material for a non-aqueous electrolyte secondary battery according to any one of (1) to (3) .
(6) A nonaqueous electrolyte secondary battery comprising the electrode for nonaqueous electrolyte secondary battery according to (5) .

By using the active material of the present invention (1), (2) and (4) and the active material produced by the production method of (5), a non-aqueous electrolyte having excellent high rate discharge characteristics (particularly cycle characteristics) A secondary battery can be provided.
By using the active material of the present invention (3), a nonaqueous electrolyte secondary battery excellent in output characteristics in addition to high rate discharge characteristics can be provided.
According to the present invention (6) and (7), it is possible to provide a nonaqueous electrolyte secondary battery electrode and a nonaqueous electrolyte secondary battery excellent in high rate discharge characteristics.

It is the schematic which shows an example of the process of manufacturing the coprecipitation precursor particle | grains of a transition metal compound with the manufacturing method of this invention. It is a figure which shows the measuring method of the starting point of the cobalt concentration gradient area | region from the particle | grain surface about the active material for nonaqueous electrolyte secondary batteries of this invention. It is a figure which shows an example of the measurement result of the starting point of the cobalt concentration gradient area | region from the particle | grain surface about the active material for nonaqueous electrolyte secondary batteries of this invention.

The composition of the lithium transition metal composite oxide contained in the active material for a non-aqueous electrolyte secondary battery according to the present invention is such that a high discharge capacity can be obtained, and the transition metal element Me containing Co, Ni and Mn, and Li In the present invention, as described below, in the active material particles, it is a so-called “lithium-excess type” which can be expressed as Li _{1 + α} Me _1-α O ₂ (α> 0). The surface and the core have different compositions, and the core is of “lithium-excess type”, but the surface (coating portion) is not “lithium-excess type”. The average composition is represented by the composition formula Li _{1 + α} Me _1-α O ₂ (Me is a transition metal containing Co, Ni and Mn, α> 0).

  The ratio of elements such as Co, Ni and Mn constituting the transition metal element constituting the lithium transition metal composite oxide can be arbitrarily selected according to required characteristics.

  In the present invention, the transition metal element Me containing Co, Ni and Mn is not uniformly distributed in one particle of the lithium transition metal composite oxide (active material). It has a core and a covering part (shell), and the Co concentration in one particle is higher in the covering part than in the core, and conversely, the Mn concentration is lower in the covering part than in the core. In order to improve the high rate discharge characteristics, the ratio of Co present in the coating is set to 3 to 10% in molar ratio with respect to the amount of transition metals present in the core (total amount of Co, Ni and Mn). It is preferable.

In order to improve the high-rate discharge cycle characteristics, it is preferable to use lithium transition metal composite oxide particles in which the Co concentration is continuously changed in one particle. Therefore, in the present invention, when the surface position of the particle is 0 and the center position is 1, the starting point of the cobalt concentration gradient region from the particle surface is 0.1 to 0.5. The core is a region where the cobalt concentration is uniform, and the covering portion is a cobalt concentration gradient region.
In the present invention, the core of the lithium transition metal composite oxide particles is expressed by Li _{1 + α} (Co, Ni, Mn) _1-α O ₂ (α> 0) because the Mn concentration is high and the Co concentration is low. This is a so-called “lithium-excess type” and shrinks during charging. On the other hand, since the coated portion of the particles has a high Co concentration and a low Mn concentration, it is a so-called “LiMeO ₂ type” represented by Li (Co, Ni, Mn) O ₂ and expands during charging. Therefore, by repeating charge and discharge, distortion occurs at the two-phase boundary between the core and the covering portion, and separation is likely to occur, but by making lithium transition metal composite oxide particles in which the two phases are continuously changed in composition, It is estimated that separation is prevented and cycle characteristics of high rate discharge are improved.

The ratio of Mn present in the core is larger in molar ratio than the total ratio of Co and Ni in that a nonaqueous electrolyte secondary battery having a large discharge capacity and excellent high rate discharge characteristics can be obtained. Preferably, the molar ratio is 62 to 72% with respect to the amount of transition metal present in the core (total amount of Co, Ni and Mn). On the other hand, the ratio of Co present in the core is preferably 2 to 23% in molar ratio with respect to the amount of the transition metal.
Moreover, it is preferable that the ratio of Mn which exists in a coating | coated part shall be 0-10% by molar ratio with respect to the quantity of the transition metal which exists in a core.

As described above, in the present invention, the composition differs between the core and the coating portion, but the core is a transition metal represented by (1 + α) / (1-α) in the composition formula Li _{1 + α} Me _1-α O ₂ . By setting the molar ratio Li / Me of Li to the element Me to be 1.2 or more or 1.6 or less, a nonaqueous electrolyte secondary battery having a large discharge capacity can be obtained. 6 is preferable. Among these, from the viewpoint that a non-aqueous electrolyte secondary battery having a particularly large discharge capacity and excellent high-rate discharge characteristics can be obtained, a battery having a Li / Me of 1.25 to 1.40 is selected. Is more preferable.

  The lithium transition metal composite oxide according to the present invention is essentially a composite oxide containing Li, Co, Ni, and Mn as metal elements, but a small amount of Na, Ca within a range not impairing the effects of the present invention. It does not exclude inclusion of other metals such as alkali metals such as alkali metals, alkaline earth metals, and transition metals represented by 3d transition metals such as Fe and Zn.

The lithium transition metal composite oxide according to the present invention has an α-NaFeO ₂ structure. The space group can be assigned to P3 ₁ 12 or R3-m. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and when ordering is recognized in the atomic arrangement in R3-m, the P3 ₁ 12 model Is adopted. Note that “R3-m” should be represented by adding a bar “-” on “3” of “R3m”.

  In the present invention, in order to improve the high rate discharge characteristic, the half width of the (104) plane when the space group by the X-ray diffraction measurement using CuKα rays is regarded as R3-m is set to 0.30. The angle is preferably 0.50 °. The half width of the (104) plane tends to increase when the firing temperature is low and decrease when the firing temperature is high. In the present invention, by baking at a temperature exceeding 700 ° C. and less than 900 ° C., the half width of the (104) plane can be easily set to 0.30 to 0.50 °.

  In the present invention, in order to improve the output characteristics as well as the high rate discharge characteristics, the average particle diameter of the lithium transition metal composite oxide particles is preferably 8 μm or less. As shown in the examples described later, in the precursor preparation step, the average particle size can be 8 μm or less by setting the stirring continuation time after the raw material aqueous solution dropping to less than 5 h. When the average particle diameter exceeds 8 μm, the non-aqueous electrolyte secondary battery using the same has a small initial high-rate discharge capacity, but is excellent in high-rate discharge cycle characteristics.

Next, a method for producing the active material for a nonaqueous electrolyte secondary battery of the present invention will be described.
In the method for producing an active material for a non-aqueous electrolyte secondary battery according to the present invention, when producing a lithium transition metal composite oxide, a coprecipitation precursor is prepared from a first aqueous solution of a transition metal compound containing Co, Ni and Mn. In the course of manufacturing, a second aqueous solution of a transition metal compound containing Co, Ni, and Mn, having a higher Co concentration than the first aqueous solution and a lower Mn concentration is added, and a Co concentration gradient region from the particle surface is formed. The process includes a step of preparing co-precipitated particles of the transition metal compound present, and a step of mixing the co-precipitated precursor particles of the transition metal compound with a Li compound and baking.
A process for producing coprecipitation precursor particles of a transition metal compound by the production method of the present invention is shown in FIG.

As an example, the following method can be employed.
A solution in a first container containing a first aqueous solution of a transition metal compound containing Co, Ni, and Mn is dropped into a reaction vessel for producing coprecipitated precursor particles at a specific rate, and the first container When the remaining amount of the solution reaches a specific amount, stirring of the first container is started, and the transition metal compound containing Co, Ni, and Mn having higher Co concentration and lower Mn concentration than the first aqueous solution. The solution in the second container containing the second aqueous solution is dropped into the first container at a constant rate. At this time, the above-mentioned specific speed (so that the dripping of the solution in the second container into the first container and the dripping of the solution in the first container into the reaction tank are completed almost simultaneously. The dropping rate of the solution in the first container into the reaction vessel) and the specific amount (the remaining amount of the solution in the first container) are adjusted.
Here, when the dropping of the solution in the first container into the reaction vessel is started from the point when the dropping of the solution in the first container is completed 1/2, When the surface position of the precipitated precursor particles is 0 and the center position is 1, the starting point of the cobalt concentration gradient region from the particle surface is 0.5, and the solution in the first container When the dropping of the solution in the second container to the first container is started from the time when the dropping to the reaction vessel is completed 3/4, the starting point of the cobalt concentration gradient region is 0.25. When the dropping of the solution in the first container into the first container is started from the point when the dropping of the solution in the first container into the reaction vessel is completed 7/8 In this case, the starting point of the cobalt concentration gradient region is 0.125. As described above, when the surface position of the coprecipitated precursor particles is 0 and the center position is 1, the starting point of the cobalt concentration gradient region from the particle surface is 0.1 to 0.5. Coprecipitated precursor particles can be produced, and lithium transition metal composite oxide particles having a similar structure can be produced using the coprecipitated precursor particles.

In preparing the coprecipitation precursor core particles by dropping the first aqueous solution, Mn is easily oxidized among Co, Ni, and Mn, and the coprecipitation precursor in which Co, Ni, and Mn are uniformly distributed in a divalent state. Since it is not easy to produce body core particles, uniform mixing at the atomic level of Co, Ni, and Mn tends to be insufficient. In particular, in the composition range of the examples described later, since the Mn ratio is higher than the Co and Ni ratios, it is preferable to remove dissolved oxygen in the aqueous solution. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used. Among them, when producing a coprecipitation precursor of transition metal carbonate as in the examples, when carbon dioxide is employed as a gas not containing oxygen, an environment in which carbonate is more easily generated is given. preferable.

Although the pH in the step of producing a precursor by co-precipitation of a compound containing Co, Ni and Mn in a solution is not limited, an attempt is made to prepare the co-precipitation precursor as a co-precipitation carbonate precursor. When it does, it can be set to 7.5-11. In order to increase the tap density, it is preferable to control the pH. By setting the pH to 9.4 or less, the tap density can be set to 1.25 g / cm ³ or more, and high-rate discharge performance can be improved. Furthermore, since the particle growth rate can be accelerated by setting the pH to 8.0 or less, the stirring continuation time after completion of dropping of the raw material aqueous solution can be shortened.

  The coprecipitation precursor core particles are preferably a compound in which Mn, Ni, and Co are uniformly mixed. In the present invention, in order to obtain an active material for a non-aqueous electrolyte secondary battery having a large discharge capacity and excellent high rate discharge characteristics, the coprecipitation precursor is preferably a carbonate. In addition, a precursor having a larger bulk density can be produced by using a crystallization reaction using a complexing agent. At that time, a higher density active material can be obtained by mixing and firing with a Li source, so that the energy density per electrode area can be improved.

  The raw materials for the coprecipitation precursor include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate, etc. as the Mn compound, and nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate as the Ni compound. As examples of the Co compound, cobalt sulfate, cobalt nitrate, cobalt acetate, and the like can be given as examples.

In the reaction crystallization method, a raw material aqueous solution of the coprecipitation precursor is supplied dropwise to a reaction tank that maintains alkalinity to obtain a coprecipitation precursor. This greatly affects the uniformity of the element distribution within one particle of the precursor. In particular, Mn is difficult to form a uniform element distribution with Co and Ni, so care must be taken. The preferred dropping rate is influenced by the reaction vessel size, stirring conditions, pH, reaction temperature, etc., but is preferably 30 ml / min or less.
In order to improve the discharge capacity, the dropping rate is preferably 10 ml / min or less, and more preferably 5 ml / min or less.

  In addition, when a complexing agent is present in the reaction tank and a certain convection condition is applied, the particle rotation and revolution in the stirring tank are promoted by continuing the stirring after the dropwise addition of the raw material aqueous solution. In this process, the particles collide with each other, and the particles are formed concentrically in a stepwise manner. That is, the coprecipitation precursor undergoes a reaction in two stages: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex is retained in the reaction tank. It is formed. Therefore, a coprecipitation precursor having a target particle size can be obtained by appropriately selecting a time for continuing stirring after the dropping of the raw material aqueous solution.

  The preferred stirring duration after completion of the raw material aqueous solution dropping is also affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., for example, when the coprecipitation precursor is carbonate, In order to grow as uniform spherical particles, 0.5 h or more is preferable, 1 h or more is more preferable, and 3 h or more is most preferable. Moreover, in order to reduce the possibility that the output performance of the battery becomes insufficient due to the particle size becoming too large, 15 h or less is preferable, 10 h or less is more preferable, and 5 h or less is most preferable.

  In the present invention, the non-aqueous solution using the active material by setting D50, which is the particle diameter at which the cumulative volume in the particle size distribution of the secondary particles of the lithium transition metal composite oxide is 50%, to 8 μm or less. The electrolyte battery improves the output characteristics in addition to the high-rate discharge characteristics, but the preferable stirring duration for setting D50 to 8 μm or less varies depending on the pH to be controlled. For example, when the pH is controlled to 8.3 to 9.0, the stirring duration is preferably 4 to 5 hours, and when the pH is controlled to 7.6 to 8.2, the stirring duration is 1 to 3 hours. Is preferred.

  The active material for a non-aqueous electrolyte secondary battery in the present invention can be suitably produced by mixing the coprecipitation precursor and the Li compound and then heat-treating them. As a Li compound, it can manufacture suitably by using lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, etc. However, with respect to the amount of the Li compound, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li compound during firing.

The firing temperature affects the reversible capacity of the active material.
When the firing temperature is too high, the obtained active material collapses with an oxygen releasing reaction, and in addition to the hexagonal crystal of the main phase, the monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type is obtained. The defined phase tends to be observed as a phase separation rather than as a solid solution phase. If too many such phase separations are contained, it is not preferable because it leads to a reduction in the reversible capacity of the active material. In such materials, impurity peaks are observed around 35 ° and 45 ° on the X-ray diffraction pattern. Therefore, the firing temperature is preferably less than the temperature at which the oxygen release reaction of the active material affects. The oxygen release temperature of the active material is approximately 1000 ° C. or higher in the composition range according to the present invention. However, there is a slight difference in the oxygen release temperature depending on the composition of the active material. It is preferable to keep it. In particular, it is confirmed that the oxygen release temperature of the precursor shifts to the lower temperature side as the amount of Co contained in the sample increases. As a method for confirming the oxygen release temperature of the active material, a mixture of a coprecipitation precursor and a lithium compound may be subjected to thermogravimetric analysis (DTA-TG measurement) in order to simulate the firing reaction process. In this method, the platinum used in the sample chamber of the measuring instrument may be corroded by the Li component volatilized, and the instrument may be damaged. Therefore, a composition in which crystallization is advanced to some extent by adopting a firing temperature of about 500 ° C. in advance. Goods should be subjected to thermogravimetric analysis.
Moreover, in this invention, when a calcination temperature is too high, distinction of a core shell will be lost and the whole may become a uniform composition.

On the other hand, if the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In the present invention, the firing temperature is preferably at least 700 ° C. or higher. By sufficiently crystallizing, the resistance of the crystal grain boundary can be reduced and smooth lithium ion transport can be promoted.
In addition, the inventors have analyzed the half width of the diffraction peak of the active material of the present invention in detail, and in the sample synthesized at a temperature up to 750 ° C., strain remains in the lattice, and at a temperature higher than that, It was confirmed that almost all strains could be removed by synthesis. The crystallite size was increased in proportion to the increase in the synthesis temperature. Therefore, even in the composition of the active material of the present invention, a favorable discharge capacity can be obtained by aiming at a particle having almost no lattice distortion in the system and having a sufficiently grown crystallite size. Specifically, it has been found that it is preferable to employ a synthesis temperature (firing temperature) such that the strain amount affecting the lattice constant is 2% or less and the crystallite size is grown to 50 nm or more. Although changes due to expansion and contraction are observed by charging and discharging by molding these as electrodes, it is preferable as an effect that the crystallite size is maintained at 30 nm or more in the charging and discharging process. That is, an active material having a remarkably large reversible capacity can be obtained only by selecting the firing temperature as close as possible to the oxygen release temperature of the active material.

  As described above, since the preferable firing temperature varies depending on the oxygen release temperature of the active material, it is generally difficult to set a preferable range of the firing temperature, but the molar ratio Li / Me is 1.2 to 1.6. In this case, in order to make the discharge capacity sufficient and to improve the high rate discharge characteristics, the firing temperature is preferably more than 700 to less than 900 ° C., more preferably around 750 to 850 ° C.

  The nonaqueous electrolyte used for the nonaqueous electrolyte secondary battery according to the present invention is not limited, and those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the nonaqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr. , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ , NClO ₄ , (n− _{C 4 H 9) 4 NI,} (C 2 H 5) 4 N-ma _{eate, (C 2 H 5)} 4 N-benzoate, (C 2 H 5) 4 N-phtalate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts of lithium dodecyl benzene sulfonate, and the like. These These ionic compounds can be used alone or in admixture of two or more.

Furthermore, by mixing and using LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced. The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to 2 in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. .5 mol / l.

The negative electrode material is not limited, and any negative electrode material that can deposit or occlude lithium ions may be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, lithium alloys (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

  It is desirable that the positive electrode active material powder and the negative electrode material powder have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituents.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material can be included as one kind or a mixture thereof. .

  Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight, and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black by pulverizing into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  The binder is usually a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

  As the filler, any material that does not adversely affect the battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are prepared by mixing the main constituents (positive electrode active material in the positive electrode, negative electrode material in the negative electrode) and other materials into a mixture and mixing with an organic solvent such as N-methylpyrrolidone or toluene or water. After that, the obtained liquid mixture is applied on a current collector described in detail below, or pressed and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. . About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

  As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a nonaqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  The configuration of the nonaqueous electrolyte secondary battery is not particularly limited, and examples thereof include a cylindrical battery having a positive electrode, a negative electrode, and a roll separator, a square battery, and a flat battery.

Both the conventional positive electrode active material and the active material of the present invention can be charged / discharged when the positive electrode potential reaches around 4.5 V (vs. Li ^/ Li ⁺ ). However, depending on the type of nonaqueous electrolyte used, if the positive electrode potential during charging is too high, the nonaqueous electrolyte may be oxidized and decomposed, resulting in a decrease in battery performance. Therefore, even when a charging method is employed such that the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or lower during use, a sufficient discharge capacity can be obtained. Secondary batteries may be required. When the active material of the present invention is used, for example, 4.4 V (vs. Li ^/ Li) such that the maximum potential of the positive electrode during charging is lower than 4.5 V (vs. Li ^/ Li ⁺ ) during use. ⁺ ) Or less and 4.3 V (vs. Li ^/ Li ⁺ ) or less, even if a charging method is adopted, it is possible to take out a discharge electric quantity exceeding the capacity of the conventional positive electrode active material of about 200 mAh / g or more. Is possible.

In order for the positive electrode active material according to the present invention to have a high discharge capacity, the transition metal element constituting the lithium transition metal composite oxide is present in a portion other than the transition metal site of the layered rock salt type crystal structure. It is preferable that the ratio is small. This is because, in the precursor to be subjected to the firing step, the transition metal elements such as Co, Ni, and Mn in the precursor core particles are sufficiently uniformly distributed, and appropriate for promoting the crystallization of the active material sample. This can be achieved by selecting the conditions for the firing process. If the distribution of the transition metal in the precursor core particles subjected to the firing step is not uniform, a sufficient discharge capacity cannot be obtained. Although the reason for this is not necessarily clear, when the distribution of the transition metal in the precursor core particles to be subjected to the firing step is not uniform, the resulting lithium transition metal composite oxide has a layered rock salt type crystal structure other than the transition metal site. The present inventors speculate that this is due to the occurrence of so-called cation mixing, in which a part of the transition metal element is present at the lithium site. The same inference can be applied to the crystallization process in the firing step. If the crystallization of the active material sample is insufficient, cation mixing in the layered rock salt type crystal structure is likely to occur. When the distribution uniformity of the transition metal element is high, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane when the X-ray diffraction measurement result belongs to the space group R3-m is large. Tend. In the present invention, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is preferably I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.0. Further, it is preferable that I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1 in the state after the discharge after charging and discharging. If the precursor synthesis conditions and procedure are inadequate, the peak intensity ratio will be smaller and often less than 1.
By adopting the synthesis conditions and synthesis procedures described in the present specification, a high-performance positive electrode active material as described above can be obtained. In particular, when the charge upper limit potential is set lower than 4.5V, for example, when a charge upper limit potential such as 4.4V or 4.3V is set, a high discharge capacity can be obtained. It can be.

  As an Example, the manufacture example of the active material for nonaqueous electrolyte secondary batteries for obtaining the active material particle in which Co density | concentration changed continuously within one particle is shown.

Example 1
[Precursor production process]
Cobalt sulfate heptahydrate, nickel sulfate hexahydrate and manganese sulfate pentahydrate were dissolved in 200 ml of ion-exchanged water, and the molar ratio of Co: Ni: Mn was 12.5: 19.94: 67.56. A 2.00 mol / l aqueous sulfate solution was prepared. This is referred to as a “first sulfate aqueous solution”.

  Cobalt sulfate heptahydrate, nickel sulfate hexahydrate and manganese sulfate pentahydrate were dissolved in 200 ml of ion-exchanged water, and the molar ratio of Co: Ni: Mn was 66.67: 16.67: 16.67. A 0.20 mol / l sulfate aqueous solution was prepared. This is referred to as “second aqueous sulfate solution”.

750 ml of ion exchange water was poured into a ₂ L reaction tank, and CO ₂ gas was bubbled for 30 min to dissolve CO _{2 in} ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.).
Stirring in the reaction vessel was started at a rotation speed of 700 rpm using a paddle blade equipped with a stirring motor. Thereafter, until the dropping of all the aqueous solution to the reaction vessel is completed, the pH in the reaction vessel is adjusted by appropriately dropping an aqueous solution containing 2.00 mol / l sodium carbonate aqueous solution and 0.4 mol / l ammonia. It was controlled so as to always maintain 7.9 (± 0.05).

  The solution in the first beaker containing the “first sulfate aqueous solution” was dropped into the reaction vessel at a rate of 4.5 ml / min using a liquid feed pump. When the remaining amount of the solution in the first beaker reaches 100 ml, stirring of the first beaker is started, and the solution in the second beaker containing the “second aqueous sulfate solution” The solution was dropped into the first beaker at a rate of 3 ml / min using a liquid feed pump. As a result, the dropping of the solution in the second beaker into the first beaker and the dropping of the solution in the first beaker into the reaction vessel were completed almost simultaneously. After completion of the dropping, stirring in the reaction vessel was continued for 3 hours. After the stirring was stopped, the mixture was allowed to stand for 12 hours or more.

  Next, using a suction filtration device, the coprecipitated carbonate particles produced in the reaction vessel are separated, and sodium ions adhering to the particles are washed away using ion-exchanged water, and then a dryer is used. Then, it was dried in an air atmosphere at 80 ° C. under normal pressure for 20 hours. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a coprecipitated carbonate precursor was produced.

[Baking process]
To 2.286 g of the coprecipitated carbonate precursor, 0.960 g of lithium carbonate is added and mixed well using a smoked automatic mortar. The molar ratio of Li: (Co, Ni, Mn) is 128.4: 100. A mixed powder was prepared. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 2 g. One pellet was placed on an alumina boat having a total length of about 100 mm and placed in a box-type electric furnace (model number: AMF20). The temperature was raised from normal temperature to 800 ° C. in an air atmosphere over about 10 hours. (The heating rate was 80 ° C./h), and calcined at 800 ° C. for 4 hours. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. In this way, a lithium transition metal composite oxide according to Example 1 was produced.

(Example 2)
In the precursor preparation step, the solution in the first beaker containing the “first aqueous sulfate solution” is dropped into the reaction vessel at a rate of 3.75 ml / min using a liquid feed pump, and the first When the remaining amount of the solution in one beaker reaches 50 ml, the solution in the second beaker containing the “second sulfate aqueous solution” is fed at a rate of 3 ml / min using a liquid feed pump. A lithium transition metal composite oxide according to Example 2 was produced in the same manner as in Example 1 except that it was dropped into the first beaker.

(Example 3)
In the precursor preparation step, the solution in the first beaker containing the “first aqueous sulfate solution” is dropped into the reaction vessel at a rate of 3.375 ml / min using a liquid feed pump, and the first When the remaining amount of the solution in one beaker reaches 25 ml, the solution in the second beaker containing the “second sulfate aqueous solution” is fed at a rate of 3 ml / min using a liquid feed pump. A lithium transition metal composite oxide according to Example 3 was produced in the same manner as in Example 1 except that it was dropped into the first beaker.

Example 4
In the precursor preparation step, a 0.40 mol / l sulfate aqueous solution having a Co: Ni: Mn molar ratio of 66.67: 16.67: 16.67 was used as the “second sulfate aqueous solution”. In the same manner as in Example 2, except that a mixed powder having a molar ratio of Li: (Co, Ni, Mn) of 126.9: 100 was prepared in the firing step. 4 produced a lithium transition metal composite oxide.

(Example 5)
In the precursor preparation step, as the “first sulfate aqueous solution”, the molar ratio of Co: Ni: Mn was set to 12.5: 18.0: 69.5, and in the firing step, Li: (Co , Ni, Mn) A lithium transition metal composite oxide according to Example 5 was produced in the same manner as in Example 2 except that a mixed powder having a molar ratio of 123.5: 100 was prepared. .

(Example 6)
In the precursor preparation process, a 0.20 mol / l sulfate aqueous solution having a Co: Ni: Mn molar ratio of 50.0: 30.0: 20.0 was used as the “second sulfate aqueous solution”. In the same manner as in Example 2, except that a mixed powder having a molar ratio of Li: (Co, Ni, Mn) of 128.4: 100 was prepared in the firing step. 6 produced a lithium transition metal composite oxide.

(Example 7)
In the precursor preparation step, after completion of dropping, the time for further stirring in the reaction vessel was set to 1 h, and in the firing step, the molar ratio of Li: (Co, Ni, Mn) was 128.4: 100. A lithium transition metal composite oxide according to Example 7 was produced in the same manner as in Example 2 except that the mixed powder was prepared.

(Example 8)
In the precursor preparation step, the lithium transition metal composite oxide according to Example 8 was prepared in the same manner as in Example 2 except that the time for further stirring in the reaction vessel was 5 h after the completion of the dropping. Produced.

Example 9
In the precursor preparation step, the lithium transition metal composite oxide according to Example 9 was prepared in the same manner as in Example 2 except that the time during which stirring in the reaction vessel was further continued was 10 h after completion of the dropping. Produced.

(Comparative Example 1)
Cobalt sulfate heptahydrate, nickel sulfate hexahydrate and manganese sulfate pentahydrate were dissolved in 200 ml of ion-exchanged water, and the molar ratio of Co: Ni: Mn was 12.5: 19.94: 67.56. A 2.00 mol / l aqueous sulfate solution was prepared.

750 ml of ion exchange water was poured into a ₂ L reaction tank, and CO ₂ gas was bubbled for 30 min to dissolve CO _{2 in} ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.).
Stirring in the reaction vessel was started at a rotation speed of 700 rpm using a paddle blade equipped with a stirring motor. Thereafter, until the dropping of all the aqueous solution to the reaction vessel is completed, the pH in the reaction vessel is adjusted by appropriately dropping an aqueous solution containing 2.00 mol / l sodium carbonate aqueous solution and 0.4 mol / l ammonia. It was controlled so as to always maintain 7.9 (± 0.05).

  The solution in the first beaker containing the aqueous sulfate solution was dropped into the reaction vessel at a rate of 3 ml / min using a liquid feed pump. After the total amount of the sulfate aqueous solution was dropped, stirring in the reaction vessel was further continued for 3 hours.

  Next, using a suction filtration device, the coprecipitated carbonate particles produced in the reaction vessel are separated, and sodium ions adhering to the particles are washed away using ion-exchanged water, and then a dryer is used. Then, it was dried in an air atmosphere at 80 ° C. under normal pressure for 20 hours. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a coprecipitated carbonate precursor was produced.

  In the firing step, 2.278 g of the coprecipitated carbonate precursor and 0.970 g of lithium carbonate were mixed to prepare a mixed powder in which the molar ratio of Li: (Co, Ni, Mn) was 130: 100. A lithium transition metal composite oxide according to Comparative Example 1 was produced in the same manner as in Example 1 except that.

(Comparative Example 2)
In the precursor preparation step, the solution in the first beaker containing the “first aqueous sulfate solution” is dropped into the reaction vessel at a rate of 6 ml / min using a liquid feed pump, and the dropping starts. At the same time, except that the solution in the second beaker containing the “second sulfate aqueous solution” was dropped into the first beaker at a rate of 3 ml / min using a feed pump. In the same manner as in Example 1, a lithium transition metal composite oxide according to Comparative Example 2 was produced.

<Measurement of half width of (104) plane by X-ray diffraction measurement>
The lithium transition metal composite oxides of Examples 1 to 8 and Comparative Examples 1 and 2 were subjected to X-ray diffraction measurement using Rigaku “MiniFlex II”. The radiation source was CuKα, and the acceleration voltage and current were 30 kV and 15 mA, respectively. About the obtained X-ray-diffraction data, the half value width was determined about the diffraction peak which exists in 44-45 degree vicinity using "PDXA" which is the attached software of the said measuring apparatus.

<Measurement of Co concentration gradient region from particle surface>
For each of the lithium transition metal composite oxides according to Examples 1 to 9 and Comparative Examples 1 and 2, a scanning electron microscope (SEM) (manufactured by JEOL, model number JSM-6360) and the energy dispersion type attached thereto Using an X-ray analysis (EDX: Energy dispersive X-ray spectrometry) apparatus (hereinafter also referred to as “SEM-EDX apparatus”), the metal composition ratio from the particle surface to the inside of the particle was measured by the following procedure.

In a ring made of acrylic resin (outer diameter: 10 mm, inner diameter: 8 mm), an appropriate amount of lithium transition metal composite oxide powder particles to be measured is collected with a spatula and charged, and then a two-part epoxy resin for curing is poured. And cured. Next, using a polishing machine (GPM GRINDING & POLISHING made by Wingo Seiki) and Emily abrasive paper (# 180), the powder particles are polished so that the cross section of the powder particles appears, and finally Emily abrasive paper (# 1000) is removed. Using this, surface polishing was performed. Platinum deposition was performed on the polished surface and set in the SEM-EDX apparatus. The working distance at the analysis position was 10 mm, and the acceleration voltage of the electron gun was 15 kV. By SEM observation, a particle suitable for cross-sectional observation and having a cross-section including the center of the particle exposed on the observation surface was selected. The analysis target elements were Co, Ni, and Mn. As shown in FIG. 2, each region distance of 8 equal parts from the center of the particle to the surface of the particle as a measuring point at each measuring point, Co, Co to the total of the molar concentration of Ni and Mn, Ni and The ratio of each Mn molar concentration was calculated.

As an example, the measurement results for the lithium transition metal composite oxide according to Example 2 are shown in FIG. Next, the procedure for obtaining the “starting point of the cobalt concentration gradient region from the particle surface” will be described using FIG. 2 as an example. In FIG. 2, when the central part of the particle is Point 1 and the surface part of the particle is Point 8 in each of the eight divided regions, cobalt (Co) is formed from Point 8 on the particle surface to Point 6 inside the particle. The concentration ratio gradually decreases, and the concentration ratio of each analysis target element is constant from the point 5 to the point 1 which is the center of the particle. In this case, Point 8 to Point 6 are defined as “cobalt concentration gradient region from the particle surface”. Thus, when it is determined that the “cobalt concentration gradient region” is from Point 8 to Point x, the value obtained according to the following equation is defined as “the start point of the cobalt concentration gradient region from the particle surface”.
Starting point of cobalt concentration gradient region from particle surface = (8−x) / 8
Therefore, in the example of FIG. 3, the value of “starting point of cobalt (Co) concentration gradient region from particle surface” is 0.250.

<Measurement of particle size>
The lithium transition metal composite oxides according to Examples 1 to 9 and Comparative Examples 1 and 2 were subjected to particle size distribution measurement according to the following conditions and procedures. Microtrac (model number: MT3000) manufactured by Nikkiso Co., Ltd. was used as a measuring device. The measuring apparatus is composed of a computer equipped with an optical bench, a sample supply unit, and control software, and a wet cell equipped with a laser light transmission window is installed on the optical bench. The measurement principle is a method in which a wet cell in which a dispersion liquid in which a sample to be measured is dispersed in a dispersion solvent circulates is irradiated with laser light, and the scattered light distribution from the measurement sample is converted into a particle size distribution. The dispersion is stored in a sample supply unit and circulated and supplied to a wet cell by a pump. The sample supply unit is always subjected to ultrasonic vibration. Water was used as a dispersion solvent. Microtrac DHS for Win98 (MT3000) was used as measurement control software. For the `` substance information '' set and input to the measuring device, set 1.33 as the `` refractive index '' of the solvent, select `` TRANSPARENT '' as the `` transparency '', and set `` non-spherical '' as the `` spherical particle '' Selected. Prior to sample measurement, perform “Set Zero” operation. The “Set Zero” operation is an operation to subtract the influence of disturbance elements other than the scattered light from the particles (glass, dirt on the glass wall surface, glass irregularities, etc.) on the subsequent measurement. Only a certain amount of water is put in, a background measurement is performed in a state where only the water as the dispersion solvent is circulating in the wet cell, and the background data is stored in the computer. Subsequently, “Sample LD (Sample Loading)” operation is performed. The Sample LD operation is an operation for optimizing the sample concentration in the dispersion that is circulated and supplied to the wet cell during measurement, and manually reaches the optimum amount of the sample to be measured in the sample supply unit according to the instructions of the measurement control software. It is an operation to throw up. Subsequently, the measurement operation is performed by pressing the “Measure” button. The measurement operation is repeated twice, and the measurement result is output from the control computer as the average value. The measurement results are as a particle size distribution histogram and values of D10, D50 and D90 (D10, D50 and D90 are particle sizes at which the cumulative volume in the particle size distribution of the secondary particles is 10%, 50% and 90%, respectively) To be acquired. The measured D50 values are shown in Table 1.

<Preparation and evaluation of nonaqueous electrolyte secondary battery>
Using each of the lithium transition metal composite oxides of Examples 1 to 9 and Comparative Examples 1 and 2 as a positive electrode active material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery was produced by the following procedure, and the battery The characteristics were evaluated.

  The positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) were mixed at a mass ratio of 85: 8: 7. This mixture was kneaded and dispersed by adding N-methylpyrrolidone as a dispersion medium to prepare a coating solution. In addition, about PVdF, it converted into solid mass by using the liquid by which solid content was melt | dissolved and dispersed. The coating solution was applied to an aluminum foil current collector having a thickness of 20 μm to produce a positive electrode plate.

  Lithium metal was used for the counter electrode (negative electrode) in order to observe the single behavior of the positive electrode. This lithium metal was adhered to a nickel foil current collector. However, preparation was performed such that the capacity of the nonaqueous electrolyte secondary battery was sufficiently positive electrode regulated.

As the electrolytic solution, a solution obtained by dissolving LiPF ₆ in a mixed solvent having a volume ratio of EC / EMC / DMC of 6: 7: 7 so that its concentration becomes 1 mol / l was used. As the separator, a microporous membrane made of polypropylene, whose electrolyte retention was improved by surface modification with polyacrylate, was used. Moreover, what adhered lithium metal foil to the nickel plate was used as a reference electrode. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) was used for the outer package. The electrode was accommodated in this exterior body so that the open ends of the positive electrode terminal, the negative electrode terminal, and the reference electrode terminal were exposed to the outside. The fusion allowance in which the inner surfaces of the metal resin composite film face each other was hermetically sealed except for the portion to be the injection hole.

  The initial charge / discharge process of 2 cycles was implemented at 25 degreeC with respect to the nonaqueous electrolyte secondary battery produced as mentioned above. All voltage control was performed on the positive electrode potential. The charging was constant current constant voltage charging with a current of 0.1 CmA and a voltage of 4.6V. The charge termination condition was the time when the current value attenuated to 0.02 CmA. The discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. In all cycles, a 30 minute rest period was set after charging and after discharging. Thus, the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example was completed.

The completed nonaqueous electrolyte secondary battery was charged and discharged for 3 cycles. All voltage control was performed on the positive electrode potential. The conditions for this charge / discharge cycle are the same as the conditions for the initial charge / discharge step, except that the charge voltage was 4.3 V (vs. Li ^/ Li ⁺ ). In all cycles, a 30 minute rest period was set after charging and after discharging. Here, the discharge capacity at the third cycle was recorded as “discharge capacity (0.1 C) (mAh / g)”.

[High rate discharge test]
Next, a high rate discharge test was performed according to the following procedure. First, constant current / constant voltage charging with a current of 0.1 CmA and a voltage of 4.3 V was performed. After a 30-minute pause, a constant current discharge with a current of 1 CmA and a final voltage of 2.0 V was performed, and the discharge capacity at this time was recorded as “initial high rate discharge capacity (mAh / g)”.
The ratio of “initial high rate discharge capacity (mAh / g)” to “discharge capacity (0.1 C) (mAh / g)” was recorded as “high rate discharge characteristics (%)”.
The above high rate discharge test is performed for 30 cycles, and the ratio of the high rate discharge capacity after 30 cycles to the “initial high rate discharge capacity (mAh / g)” is defined as “high rate discharge capacity maintenance rate after 30 cycles (%)”. Recorded.

[Output performance test in low SOC range]
After the high-rate discharge test, constant current and constant voltage charging with a current of 0.1 CmA and a voltage of 4.3 V was performed, and the amount of charge at this time was measured. After a 30-minute pause, a constant current discharge with a current of 0.1 CmA was performed, and the discharge was paused when 70% of the amount of electricity was applied to the amount of charge.

30 minutes after the discharge was stopped, a test was performed in which discharge was performed at each rate discharge current for 1 second. Specifically, first, discharging was performed for 1 second at a current of 0.1 CmA, and after a pause of 2 minutes, supplementary charging was performed for 1 second at a current of 0.1 CmA. Further, after a rest of 2 minutes, the battery was discharged for 1 second at a current of 1 CmA, and after a rest of 2 minutes, supplementary charging was performed for 10 seconds at a current of 0.1 CmA. Further, after a rest of 2 minutes, the battery was discharged at a current of 2 CmA for 1 second, and after a rest of 2 minutes, a supplementary charge was performed at a current of 0.1 CmA for 20 seconds. From the above results, the voltage drop after 1 second of each rate discharge is plotted against the current value, and fitting by the least square method is performed. From the intercept and slope of this graph, pseudo values at the discharge rate of 0 are obtained. A certain E0 and DC resistance R were calculated. Assuming a discharge end voltage of 2.5 V, the output at SOC 30% was obtained by the following equation. This result was recorded as “initial output (W)”.
SOC 30% output (W) = 2.5 x (E0-2.5) / R
The output performance test was performed for 30 cycles, and the ratio of the output after 30 cycles to the “initial output (W)” was recorded as “output maintenance rate after 30 cycles (%)”.

  For Examples 1 to 9 and Comparative Examples 1 and 2, the measurement results of (104) half width, initial efficiency discharge capacity, initial output, high-rate discharge capacity maintenance rate after 30 cycles, and output maintenance rate after 30 cycles are shown in Table 1. Shown in Further, Table 1 also shows the measurement results obtained by the above-mentioned “Measurement of Co concentration gradient region from particle surface”.

From the example of FIG. 3 and the result of Table 1, the metal composition from the particle surface to the inside of the particles of the lithium transition metal composite oxides according to Examples 1 to 9 and Comparative Examples 1 and 2 are both coprecipitated carbonates. The metal composition ratio of the “first sulfate aqueous solution” and “second sulfate aqueous solution” used in the step of preparing the precursor, and the dropping procedure of these sulfate aqueous solutions into the reaction tank were reflected as they were. I found out that it was a thing.
That is, in Examples 1 to 9, when preparing the coprecipitated carbonate precursor, the solution in the first beaker (first sulfate aqueous solution containing Co, Ni and Mn) was dropped into the reaction vessel. Of the solution in the second beaker (second sulfate aqueous solution containing Co, Ni and Mn having a higher Co concentration and lower Mn concentration than the first sulfate aqueous solution) By starting dropping into the first beaker, a coprecipitated carbonate precursor was obtained, and this coprecipitated carbonate precursor was mixed with lithium carbonate and baked at 800 ° C. to obtain a lithium transition metal composite oxide When the particle surface position is 0 and the center position is 1, the start point of the Co concentration gradient region from the particle surface is 0.500. Similarly, when dropping is started from the end of 3/4, the starting point of the Co concentration gradient region from the particle surface is 0.250, and when dropping is started from the end of 7/8, The starting point of the Co concentration gradient region from the surface is 0.125. The molar ratio of coating portion Co / core Me is 10% in Example 4 and 5% in other examples.
And after completion | finish of dripping, when the time which further continues stirring in a reaction tank shall be less than 3h, it is a particle diameter from which the cumulative volume in the particle size distribution of the secondary particle of lithium transition metal complex oxide will be 50%. D50 is 8 μm or less. By using this as an active material, a non-aqueous electrolyte secondary battery excellent in initial high rate discharge capacity, initial output, high rate discharge capacity maintenance rate after 30 cycles, and output maintenance rate can be obtained. Obtained (Examples 1 to 7).
In addition, when the time during which stirring in the reaction vessel is further continued after the completion of dropping is set to 5 h and 10 h, the particle diameter D50 of the lithium transition metal composite oxide increases to 13 μm and 18 μm. Non-aqueous electrolyte secondary batteries (Examples 8 and 9) using this as an active material were obtained by using a uniform lithium transition metal composite oxide having no Co concentration gradient region from the particle surface (no covering portion) as an active material. Compared with the one (Comparative Example 1), the initial high rate discharge capacity is not improved, but the high rate discharge capacity retention rate is high after 30 cycles, and the cycle characteristics of high rate discharge are improved.

  Moreover, when dripping is started at the same time, a uniform lithium transition metal composite oxide is obtained, but the non-aqueous electrolyte secondary battery using this as an active material (Comparative Example 2) has a small initial high rate discharge capacity. .

  In view of the above, the lithium transition metal composite oxide having the core and the covering portion is obtained as follows. “When the covering portion has a cobalt concentration gradient, the particle surface position is 0 and the center position is 1. By satisfying the requirement that the starting point of the cobalt concentration gradient region from the surface is in the range of 0.1 to 0.5, the non-aqueous electrolyte secondary battery using this as an active material has high rate discharge characteristics and high It can be said that the cycle characteristics of rate discharge are improved. Furthermore, it can be said that the output characteristics are improved by using particles of 8 μm or less.

  Since the nonaqueous electrolyte secondary battery using the active material of the present invention has excellent high rate discharge characteristics, cycle characteristics, and output characteristics, such as power supplies for electric vehicles, power supplies for electronic devices, power supplies for power storage, etc. It can be effectively used for non-aqueous electrolyte secondary batteries.

Claims (6)

Lithium transition metal composite oxidation having an α-NaFeO ₂ type crystal structure and an average composition represented by the composition formula Li _{1 + α} Me _1-α O ₂ (Me is a transition metal containing Co, Ni and Mn, α> 0) The lithium transition metal composite oxide is a particle having a core and a coating portion, and the cobalt concentration in the coating portion is higher than the cobalt concentration in the core. High, the manganese concentration of the coating portion is lower than the manganese concentration of the core, the coating portion has a gradient of cobalt concentration, and when the surface position of the particle is 0 and the center position is 1, An active material for a non-aqueous electrolyte secondary battery, wherein the starting point of the cobalt concentration gradient region is 0.1 to 0.5.   2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a ratio of cobalt present in the coating portion is 3 to 10% in a molar ratio with respect to an amount of the transition metal present in the core. Active material.   3. The non-aqueous electrolyte secondary battery according to claim 1, wherein a particle diameter in which a cumulative volume in a particle size distribution of secondary particles of the lithium transition metal composite oxide particles is 50% is 8 μm or less. Active material. It is a manufacturing method of the active material for nonaqueous electrolyte secondary batteries of any one of Claims 1-3 , Comprising: A coprecipitation precursor from the 1st aqueous solution of the transition metal compound containing cobalt, nickel, and manganese. In the course of preparation, a second concentration of transition metal compound containing cobalt, nickel and manganese, having a higher cobalt concentration than that of the first aqueous solution and a lower manganese concentration, is added. Producing the lithium transition metal composite oxide through a step of producing coprecipitation precursor particles of an existing transition metal compound, a step of mixing the coprecipitation precursor particles with a lithium compound, and firing. A method for producing an active material for a non-aqueous electrolyte secondary battery. The electrode for nonaqueous electrolyte secondary batteries containing the active material for nonaqueous electrolyte secondary batteries of any one of Claims 1-3 . A nonaqueous electrolyte secondary battery comprising the electrode for a nonaqueous electrolyte secondary battery according to claim 5 .